In the manufacture of transparent containers such as glass bottles, various types of checks or defects may occur in the sidewalls of the containers. These checks or defects, termed "commercial variations" in the art, can affect commercial acceptability of the containers. The commercial variations may be opaque, such as stones, or may be refractive such as blisters, bubbles or tears.
It has heretofore been proposed to employ electro-optical inspection systems for detecting commercial variations that affect optical properties of the containers. The basic principle is that a light source is positioned on one side of the container and a camera is positioned on the other. The light source may be configured to have an intensity that varies across one dimension of the source. Light rays normally travel from the source straight through the container sidewall and are then focused onto the camera, and are viewed at the camera at a given intensity. However, a refractive commercial variation bends the light ray as it travels through the container sidewall, so that the image projected onto the camera is of a different area of the light source. If such different area has a different intensity than the area normally imaged onto the camera, the camera can detect the refractive sidewall defect.
U.S. Pat. No. 4,610,542 discloses one technique for varying the effective intensity of the light source across the light source. An elongated filament lamp is positioned along the upper edge of a diffuser plate to produce an intensity gradient in the vertical direction across the light source. The upper area of the diffuser plate is brightest, the middle area has average brightness and the lower area is darkest. U.S. Pat. No. 4,601,395 discloses another technique in which a filter is placed across the light source diffuser screen to provide differing areas of effective light source intensity.
Although the systems disclosed in the noted patents, both of which are assigned to the assignee hereof, address problems theretofore extant in the art, further improvements remain desirable. In particular, it is desirable to provide a larger area of contrast associated with refractive commercial variations so as to enhance the probability of detecting relatively small variations such as bird swings, enlargements or mounds that surround small stones, and settle waves that frequently occur in blow-and-blow glassware manufacturing processes. It is a general object of the present invention to provide an inspection apparatus and method that accomplish this objective. Another object of the present invention is to provide an apparatus and method for inspecting transparent containers of the type described above in which the filter mechanism placed across the light source for creating the light source intensity gradient is of inexpensive manufacture.